Conventionally, it has been proposed a fluorescent display tube with a touch panel in which an anode electrode is formed on one substrate of an outer housing made of a glass substrate, and a touch electrode is formed on the other substrate opposite to the one substrate (for example, see PTL 1). The conventional fluorescent display tube with a touch switch will be explained with reference to FIGS. 5A and 5B. FIG. 5A is a plan view viewed in YO direction of FIG. 5B, and showing a positional relationship of electrodes. FIG. 5B is a sectional view taken on line Y1-Y1 in an arrow direction. The outer housing is defined by a front substrate 11 and a rear substrate 12 facing to each other, and a sideboard 13 (side member) interposed between both substrates. An anode electrode 21 is formed on an inner wall of the rear substrate 12. A touch electrode 22 (touch detection electrode) and a dummy electrode 24 are formed on an inner wall of the front substrate 11. Incidentally, a fluorescent film is formed on the anode electrode 21. However, the fluorescent film is omitted in figures. The outer housing is provided with a filament F (cathode) emitting electron as an electron source, a control electrode G, a shield electrode 23, a lead wire 25 for the front substrate, and the like. The shield electrode 23 is interposed between the touch electrode 22 and the filament F.
The anode electrode 21, the touch electrode 22, and the dummy electrode 24 are made of metal film such as aluminum. The touch electrode 22 and the dummy electrode 24 have a slit-shaped opening or are formed in a mesh shape, and thereby they are translucent. The shield electrode 23 and the control electrode G are formed in a mesh shape, and thereby translucent. The anode electrode 21 is so arranged as to be able to display three types of character patterns, HDD, USB, and FD. The touch electrode 22 is so arranged as to be vertically overlapped with the anode electrode 21 which forms various character patterns when viewed in YO direction in FIG. 5B.
Next, an operating principle of a touch switch of the fluorescent display tube with a touch switch shown in FIG. 5 and a control device thereof will be explained with reference to FIGS. 6A and 6B. In FIG. 6A, when a pulse is supplied from a pulse generation circuit 261 to a condenser C, a comparator 262 detects an electrostatic capacity of the condenser C. In this condition, when a finger 263 of an operator touches (approaches) a touch electrode 22, an electrostatic capacity is generated between the touch electrode 22 and the finger 263, and the comparator 262 detects the electrostatic capacity. The comparator 262 generates an output corresponding to imbalance between both electrostatic capacities. Namely, the comparator 262 detects a touch of the finger 263, and generates the output. In FIG. 6B, when the comparator 262 detects the touch of the finger 263, a touch detection switch control section 271 send a control signal corresponding to the touch electrode 22 to a control device 274 and to a display control section 272. The display control section 272 controls lighting on/off of the anode electrode 21 of a display section 273 corresponding to the control signal. Namely, the anode electrode 21 opposite to the touch electrode 22 on which the finger 263 touches is changed lighting on or off.